Corticotropin Releasing Factor plays key roles in the modulation of adaptive responses of the endocrine, central nervous and immune systems to stress. In previous granting periods, this Project characterized CRF and cloned the first CRF receptor (CRF-R), a G-protein coupled receptor linked to adenylate cyclase. Evidence derived from receptor chimeras and mutants point to the importance of the first extracellular domain of the receptor for initial ligand binding but not for receptor activation. We propose to characterize binding sites within the first extracellular domain of the receptor and to explore hypotheses regarding independent or ligand-dependent persistent activities that we have observed with wild type receptors or ligand/receptor chimeras. Since submission of the last competitive proposal, we and others have identified receptors derived from a second gene, CRF-R2, which surprisingly had only modest affinity for CRF, but high affinity for CRF- related peptides from lower vertebrates, urotensin and sauvagine. A novel CRF-related peptide, which we named urocortin, was then cloned from rat midbrain and human genomic libraries; the synthetic replicate has high affinity and can functionally stimulate both type 1 and 2 CRF receptors in vitro and in vivo. We have anatomic and immunologic evidence for the existence of additional ligands related to urotensin and sauvagine within the pituitary where we will focus on paracrine interactions. Finally, we will extend observations of altered urocortin and CRF-R2 and its known and unknown ligand(s) will e explored within the pituitary where we will focus on paracrine interactions. Finally, we will extend observations of altered urocortin and CRF-R2 expression in different satiety states and explore the importance of this receptor and its ligand sin mediating central responses to leptin. In the context of the Program, progress in this Project should continue to yield information concerning the molecular nature, regulation and physiologic roles of ligands and receptors of the CRF family and provide insight regarding endocrine, metabolic and stress-related diseases.